All of us faced those situations where you want to use WebParts that you used to use in SharePoint 2010 but all of the sudden disappeared in SharePoint 2013.
One of those web parts are the well-known OWA webparts ; To be able to add these web parts , do the following:-
1- Site Settings -> Web parts
2- Add new Document -> Navigate to Microsoft.SharePoint.Portal.WebControls.OWAPart and select it
3- Finally click on Populate Out
4- Et Voila ! you can create a new page , insert a new web part under Miscellaneous Category you will find the OWA web part.